The invention relates to a method and apparatus for detecting the presence of an ophthalmic lens, particularly a contact lens, in a package. The method for detecting the presence of an ophthalmic lens, particularly a contact lens, in a package, is characterised in that the package is checked for presence of an ophthalmic lens with an x-ray detection system and with an optical detection system, whereby presence of an ophthalmic lens is given if either one or both cameras detect presence of an ophthalmic lens.
Ophthalmic lenses are usually placed in a package for storage and for transport. The preferred packages are so-called blister packages. A blister package consists of a plastic container, for example made of polypropylene (PP), the top of which is sealed with a film (plastic or composite material) after the ophthalmic lens has been placed in the plastic container.
In particular, contact lenses that are produced in large unit numbers, for example disposable contact lenses, are sealed into blister packages. Such contact lenses are preferably manufactured by fully automated so-called mould or full-mould processes. The contact lenses produced in this manner are moulded parts usually having little mechanical stability and a water content of more than 60% by weight. After manufacture, the lens is usually checked for defects, then packaged and subjected to heat sterilisation at 121° C. in an autoclave.
Under certain circumstances, empty packages may appear in the process. Without checking the presence of a contact lens in each package, an empty package may be delivered to the customer, which is considered a serious quality issue in a competitive market situation. Empty packages in the process may be recognised by chance or by spot checks, with the result, that either the whole batch has to be rejected or all the contact lens packages of the batch have to undergo manual checking. Both procedures involve substantial costs and effort.
The following technical solutions are known for detecting the presence of an ophthalmic lens, particularly a contact lens, in a package:
EP0685734 A discloses a method and system for verifying the presence of a lens in a transparent package. The method comprises the steps of moving the package into an inspection position, and conducting a light beam through the package and onto an image plane to form an image of the package on the image plane. The method further comprises the steps of generating a set of signals representing the image on the image plane, and analyzing those signals to determine whether a lens is present in the package. This analyzing step includes the steps of searching the package image for images of discrete objects and for each object image found in the package image, identifying values for a plurality of parameters, and analyzing those identified values according to a predetermined procedure to identify the object as being a lens or as not being a lens. A lens present signal is generated if one object image found in the package image is identified as a lens and a lens missing signal is generated if no object images are found in the package image or if all object images found in the package image are identified as not lenses.
EP0999140 B1 discloses an apparatus for detecting the presence or position of an ophthalmic lens, such as a contact lens in saline solution, in a container using a source of electromagnetic energy in the ultraviolet range. The source of electromagnetic enemy is located relative to the container to direct ultraviolet electromagnetic energy at the container. A detector is disposed relative to the container and the source to detect the electromagnetic energy from the source which is reflected by the lens and the container. A processor is included for determining the presence or position of the lens in the container responsive to the reflection of the ultraviolet electromagnetic energy by the lens.
EP1050470 A discloses a method and a device for detecting the presence of an ophthalmic lens, particularly a contact lens, in a package. The method uses a spectroscopic process. Packages containing a contact lens have a characteristic change in their measuring spectrum compared with a package without a contact lens. By evaluating the spectra, it is possible to determine whether or not there is a contact lens in a package. The method is suitable for checking already sealed packages with the packages remaining intact.
EP1057730 A discloses a method and a device for detecting the presence of an ophthalmic lens using electromagnetic radiation of a characteristic resonance frequency of atomic groups within the object (e.g. a contact lens), in particular using near infrared radiation (NIR).
EP1109011 A discloses a method and a device for registering the presence of an ophthalmic lens, particularly a contact lens in a package. The invention solves the problem through the use of an IR camera. Packages containing a contact lens, have a change in their temperature distribution compared with a package without a contact lens. By evaluating the temperature difference directly after the procedure for filling the lens into the package, it is possible to determine whether or not there is a contact lens in a package.
JP2003267326 and JP2005121368 disclose a method capable of automating and highly accurately implementing the detection of the presence or absence of ophthalmic lenses in a housing case, the number of present ophthalmic lenses, or their types without visual inspection with human eyes. The housing case to be detected is irradiated with inspecting light of the visible light region, and transmitted light or reflected light from the housing case is imaged by a color image sensor. The presence or absence of colored ophthalmic lenses in the housing case, the number of present ophthalmic lenses, or their types are determined based on acquired R values, G values, and B values.
There are several draw backs to the methods known in the art for detecting the presence of an ophthalmic lens, particularly a contact lens, in a package. Optical detection systems, in particular in the ultraviolet or visible range of electromagnetic radiation, are suitable to detect slightly wet or dry lenses very reliable, but often fail to detect wet lenses. It is particularly difficult to differentiate between a drop of water and a wet lens in a package. Temperature systems, in particular in the infrared or near infrared range of electromagnetic radiation require extensive calibration to be reliable. Finally, imaging systems require a rather complex logical setup for reliable detection, as for each object image found in the total package image, values for a plurality of parameters have to be identified and analyzed according to a predetermined procedure to identify the object as a lens or as not a lens.
The invention is therefore based on the problem of providing a reliable and simple testing method with which it is possible to detect, at low cost and with a limited logical setup, whether an ophthalmic lens, especially a contact lens, is actually present in a package. Such method should be reliable for wet, slightly wet as well as for dry lenses.